1. Field of the Invention
The present invention relates to an image processing apparatus having a function for detecting originals containing specific patterns of monochromatic or color images, and also to a copying machine having such an image processing apparatus.
2. Description of the Related Art
Nowadays, copying machines are available which can produce color copies of extremely high quality, and this has given a rise to the demand for prevention of forgery of bills, securities and other valuable papers. To cope with this demand, it has been proposed to adopt pattern matching techniques in copying machines to detect and reject any original which should not be copied. In such a technique, the image pattern of the original input to a copying machine, after correction for any inclination in the orientation of the original, is compared with image patterns which have been registered in the machine, for the purpose of recognition and evaluation of matching of the pattern.
Image processing apparatus incorporated in known copying machines of the type described, however, does not have any means for deciding the state of the image recognition function. Therefore, when, for example, the image recognition function and the image processing apparatus are formed on different circuit boards, it is rather easy to demount the circuit board carrying the image recognition function, so that the copying machine performs the ordinary copying operation even when the original is a specific one which should not be copied. This undesirably allows easy forgery of papers such as bills and securities.
Under these circumstances, the present assignee of the invention has proposed techniques in which each copy is provided with information which indicates the fact that the copy is a copy and not an original.
One such technique is to combine a specific code or a pattern with the output image. This technique employs a function for storing a specific pattern to be added and a function for combining the pattern with the output image. In a copy produced by this technique, the specific pattern is combined with the output image by a color tone or density which is not so noticeable to human eyes but is discriminatable by a specific technique.
In this type of color copying machine, there is no means for preventing replacement of the parts carrying the pattern storage and combining functions with a part which does not have such functions. After such replacement, the pattern is not added to the output image, so that forgery can easily be done by using the copying machine.
Furthermore, since the pattern is fixedly stored in such a manner as not to be changed, it is not possible for persons such as service personnel to set different patterns on different machines to enable identification of the machine from the copy produced by the machine.
The assignee of the present invention also has proposed a method for preventing illegal copying of bills, securities and so forth which is a critical problem noticed in recent years due to the high reproducibility of original images offered by current copying machines. According to this method, data concerning specific originals such as bills and securities are beforehand stored in terms of color space. Any original set on the copying machine is rejected when this original exhibits the same distribution of data in the color space as that of one of the above-mentioned specific originals. However, known copying machines realizing such forgery prevention method do not have functions for storing data concerning illegal use of the machine, e.g., type of the original illegally copied, type of the input device and identification of the operator who made such illegal use of the machine, nor a function for informing an administrator of the fact that the copying machine has been used illegally for the purpose of copying bills or the like.
Consequently, there is no means for keeping control over the copying machine against illegal copying, particularly when the copying machine is set at a place where there is no person other than the illegal user.
As explained before, various methods have been proposed for the purpose of enabling recognition of specific originals of the kind described.
In all the proposed methods, however, the image recognition is performed by an independent circuit. Therefore, it is not impossible for those who are familiar with this type of machine to modify the machine so as to enable illegal copying of bills or the like, by demounting the circuit board carrying the image recognition function.
Full-color copying machines also have been proposed in which identification information such as the serial number of the machine is added to the copy produced by the machine. Such information is given in the form of a mark of light yellow color or specific binary pattern.
All these known copying machines, however, are still unsatisfactory in that they permit easy demounting of the image recognition or detection function, due to the fact that such a function is performed by a single circuit board which is not difficult to demount.